I'm amazed that my answer will be similar to Windrider's. A new employee of mine told me today he was amazed at how calm and happy I am, even in the middle of chaos. I told him that happiness is a choice and I choose to be happy- even with the challenges I face. I may not always show it around my wife and kids- in fact our families see us at our worst- but I try, even when my kid's are making it hard to do so. That being said, my wife and kids are my greatest joy.
That probably doesn't answer your question, Jason, so to answer it- yes, I believe that's true overall. The level of satisfaction one gets from fulfilling their purpose can only make them happier.